Meaning: When people are kind, their kindness becomes stronger and cruelty becomes weaker.
Choice of Words: Kindness is the quality of being friendly, generous, and considerate. Prevails means to be more powerful or influential than something else. Cruelty is the quality of being intentionally cruel or causing pain or suffering to others. Fades means to gradually become weaker or less visible. When you put them together, the sentence suggests that kindness has the power to overcome cruelty and create a better world.